氮掺杂石墨烯量子点/钯纳米复合材料的研究

铂基催化剂因具有高催化活性、高稳定性而成为极其重要的能源转化催化剂。本文采用水热法合成氮掺杂石墨烯量子点支撑的钯纳米复合材料(Pd@N-GQDs),并将其用于碱性介质中甲醇的电催化氧化反应。实验结果表明,相比同类型材料钯负载于石墨烯纳米片(Pd@GS)、钯负载于石墨烯量子点(Pd@GQDs)和商业钯黑催化剂(Pd@C),Pd@N-GQDs纳米材料具有很高的催化活性和稳定性,并可减少催化剂材料中贵金属的使用量。     

Palladium-containing graphene-like material: Synthesis and catalytic activity

A graphene-like material with surface amine groups is obtained by graphite oxide reduction with ethylenediamine. A catalyst for the hydrogenation of nitrocompounds and unsaturated hydrocarbons is created by depositing Pd nanoparticles on the graphene material. The aliphatic chain is found to prevent agglomeration of the graphene sheets, while the amine groups form the growth centers of palladium nanoparticles, allowing their uniform distribution and small size.     

Nitrogen-doped holey graphene nanoscrolls for high-energy and high-power supercapacitors

Porous structure and heteroatom doping are two key parameters for significantly boosting the capacitive performance of graphene-based materials.Herein,we report a facile approach to prepare onedimensional(ID) nitrogen-doped holey graphene nanoscrolls(NHGNSs) through cold quenching treatment of two-dimensional graphene oxide sheets,followed by thermal annealing in the successive atmosphere of NH_3 and air.Benefiting from the synergy of the unique 1D tubular morphology,abundant nanoholes and nitrogen doping,the NHGNSs exhibit a high specific capacitance of 126 F/g at 1 A/g in ionic liquid electrolyte and excellent rate capability with 81% of the capacitance retained at 20 A/g.Furthermore,the fabricated symmetric supercapacitors based on NHGNSs achieve both high energy density of 53.5 Wh/kg at 875 W/kg and high power density of 17.5 kW/kg at 43.4 Wh/kg.The simple synthetic process and superior electrochemical performance suggest the great potential of NHGNSs for supercapacitor application.     

Hydrogen sorption on palladium-doped sepiolite-derived carbon nanofibers

The hydrogen sorption behavior of novel Pd-doped sepiolite-derived carbon nanofibers (SDCNs) was investigated. Two chemical doping methods of ethanol/toluene reduction and a polyol process were applied to control Pd(0) formation in the SDCNs at different Pd doping levels. Hydrogen storage capacity was observed to vary depending on the Pd particle size and doping amount as the Pd particle surface area and the carbon Brunauer-Emmett-Teller (BET) surface area change with them, suggesting the existence of an optimum Pd doping level at each doping method for the best hydrogen storage capacity. Among the samples prepared using the polyol method at different Pd amounts, the maximum hydrogen uptake of about 0.41 wt % was obtained at 298 K and 90 bar for the 5 wt % Pd-doped SDCN that has a relatively high Pd particle surface area and carbon BET surface area. Samples prepared using the ethanol/toluene reduction method exhibited a higher hydrogen uptake of about 0.59 wt % at lower Pd doping levels (3 wt % Pd) due to a smaller Pd particle size and relatively high carbon BET surface area. The hydrogen desorption behavior investigated by differential scanning calorimeter exhibited that a higher amount of hydrogen desorbed at around 860 K from the Pd-doped SDCNs compared to that from the undoped SDCN. Fourier transform infrared (FTIR) spectroscopic analysis suggested that some of the weak chemisorbed hydrogen changes to a normal covalent bond during the heating and effuses at around 860 K.     

Synthesis of Nitrogen-Doped Graphene via Thermal Annealing Graphene with Urea

Chemical doping is an effective method to intrinsically modify the chemical and electronic property of graphene. We propose a novel approach to synthesize the nitrogen-doped graphene via thermal annealing graphene with urea, in which the nitrogen source can be controllably released from the urea by varying the annealed temperature and time. The doped N content and the configuration N as well as the thermal stabilities are also evaluated with X-ray photoelectron spectroscopy and Raman spectra. Electrical measurements indi-cate that the conductivity of doped graphene can be well regulated with the N content. The method is expected to produce large scale and controllable N-doped graphene sheets for a variety of potential applications.     

草簇状石墨烯片限域Pd纳米粒子及其催化应用(英文)

通过氨基离子液体改性石墨烯,并将其固载于堇青石表面,作为负载型Pd催化剂的载体.所制备的Pd催化剂经加氢老化后,表面石墨烯呈草簇状结构,将Pd纳米粒子限域于片层内,有效防止了Pd的流失和团聚.在重要的工业反应对羧基苯甲醛(4-CBA)加氢中,此结构催化剂与传统的钯碳催化剂相比,表现出很好的稳定性     

Hydrogen capacity of palladium-loaded carbon materials

Several samples of palladium-loaded single-wall carbon nanotubes and palladium-loaded MAXSORB activated carbon were prepared by means of the reaction of the raw carbon support with Pd2(dba)3.CHCl3. When carbon nanotubes were used as the support, the palladium content in the samples reached 13-31 wt % and fine particles of 5-7 nm average size were obtained. In the case of the samples with MAXSORB as the support, the palladium content was higher (30-50 wt %) and the particle size larger (32-42 nm) than in the nanotube samples. At 1 atm and room temperature, the hydrogen capacity of the palladium-loaded samples exceeds 0.1 wt % and is much higher than the capacity of the raw carbon supports (less than 0.01 wt %). The maximum hydrogen capacity at 1 atm and room temperature was found to be 0.5 wt %. A maximum hydrogen capacity of 0.7 wt % was obtained at 90 bar in a palladium-loaded MAXSORB sample, while the capacities for the raw carbon nanotubes and MAXSORB at the same pressure were 0.21 and 0.42 wt %, respectively. At low pressure, it was observed that the H/Pd atomic ratios in the palladium-loaded samples were always higher than in the bulk Pd. The spillover effect is considered as a possible cause of the high H/Pd atomic ratios. On the other hand, the effect of the pressure increase on the spillover was observed to be very low at high pressure and room temperature.     

微波固相法快速制备氮掺杂石墨烯

以鳞片石墨为原料, 首先通过Hummers法制备氧化石墨, 再将洗涤至中性的氧化石墨分散液与乙二胺反应得到功能化石墨烯。干燥后的功能化石墨烯在微波辐照下能瞬间产生高热, 促使接枝的乙二胺分子分解并实现对石墨烯原位掺杂制备出氮掺杂石墨烯。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、X射线衍射(XRD)、X射线能谱(EDS)对样品的形貌、结构和组成进行了表征。结果表明:该合成途径能成功实现对氧化石墨烯的还原和掺杂, 所合成的氮掺杂石墨烯呈现透明绢丝状结构。     

微波固相法快速制备氮掺杂石墨烯

以鳞片石墨为原料,首先通过Hummers法制备氧化石墨,再将洗涤至中性的氧化石墨分散液与乙二胺反应得到功能化石墨烯。干燥后的功能化石墨烯在微波辐照下能瞬间产生高热,促使接枝的乙二胺分子分解并实现对石墨烯原位掺杂制备出氮掺杂石墨烯。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、X射线衍射(XRD)、X射线能谱(EDS)对样品的形貌、结构和组成进行了表征。结果表明:该合成途径能成功实现对氧化石墨烯的还原和掺杂,所合成的氮掺杂石墨烯呈现透明绢丝状结构。     

Pd/Al2O3催化剂催化毛竹与聚乙烯共裂解反应研究

我们采用等体积浸渍法制备了Al2O3负载贵金属Pd系列催化剂,分别在N2和H2气氛下,研究了不同Pd负载量的催化剂对毛竹和低密度聚乙烯(LDPE)混合物的催化裂解性能.实验结果表明:Pd的负载量为1.0%时,Pd/Al2O3催化剂在两种气氛下活性均较好,在H2气氛下所得到的油品中烯烃含量较低,异链烷烃和环烷烃含量较高,油品的收率和质量均明显优于在N2气氛下所得到的油品.XRD表征发现,Pd负载量为1.0%的催化剂上,Pd在Al2O3载体上生成了晶形,表明金属钯有利于毛竹和LDPE共裂解生成液体产物.     

Effect of microstructure of nitrogen-doped graphene on oxygen reduction activity in fuel cells

The development of fuel cells as clean-energy technologies is largely limited by the prohibitive cost of the noble-metal catalysts needed for catalyzing the oxygen reduction reaction (ORR) in fuel cells. A fundamental understanding of catalyst design principle that links material structures to the catalytic activity can accelerate the search for highly active and abundant nonmetal catalysts to replace platinum. Here, we present a first-principles study of ORR on nitrogen-doped graphene in acidic environment. We demonstrate that the ORR activity primarily correlates to charge and spin densities of the graphene. The nitrogen doping and defects introduce high positive spin and/or charge densities that facilitate the ORR on graphene surface. The identified active sites are closely related to doping cluster size and dopant-defect interactions. Generally speaking, a large doping cluster size (number of N atoms >2) reduces the number of catalytic active sites per N atom. In combination with N clustering, Stone-Wales defects can strongly promote ORR. For four-electron transfer, the effective reversible potential ranges from 1.04 to 1.15 V/SHE, depending on the defects and cluster size. The catalytic properties of graphene could be optimized by introducing small N clusters in combination with material defects.     

Palladium Nanoparticles Bonded to Two‐Dimensional Iron Oxide Graphene Nanosheets: A Synergistic and Highly Reusable Catalyst for the Tsuji–Trost Reaction in Water and Air

Low cost, high activity and selectivity, convenient separation, and increased reusability are the main requirements for noble‐metal‐nanocatalyst‐catalyzed reactions. Despite tremendous efforts, developing noble‐metal nanocatalysts to meet the above requirements remains a significant challenge. Here we present a general strategy for the preparation of strongly coupled Fe₃O₄ and palladium nanoparticles (PdNPs) to graphene sheets by employing polyethyleneimine as the coupling linker. Transmission electron microscopic images show that Pd and Fe₃O₄ nanoparticles are highly dispersed on the graphene surface, and the mean particle size of Pd is around 3 nm. This nanocatalyst exhibits synergistic catalysis by Pd nanoparticles supported on reduced graphene oxide (rGO) and a tertiary amine of polyethyleneimine (Pd/Fe₃O₄/PEI/rGO) for the Tsuji–Trost reaction in water and air. For example, the reaction of ethyl acetoacetate with allyl ethyl carbonate afforded the allylated product in more than 99 % isolated yield, and the turnover frequency reached 2200 h^?1. The yield of allylated products was 66 % for Pd/rGO without polyethyleneimine. The catalyst could be readily recycled by a magnet and reused more than 30 times without appreciable loss of activity. In addition, only about 7.5 % of Pd species leached off after 20 cycles, thus rendering this catalyst safer for the environment.     

Catalytic hydrodechlorination reaction of chlorophenols by Pd nanoparticles supported on graphene

Chlorophenols are widely used as industrial chemicals such as herbicides, insecticides, wood preservatives, and disinfectants. However, chlorophenols are very toxic materials and they have become the cause of current environmental issues. Hydrodechlorination (HDC) reaction is a more environmentally friendly removal method of chlorophenols than other methods. In this paper, Pd–modified graphene was prepared and applied to HDC reaction. Pd supported on graphene (refer to Pd/G) was prepared using the recently reported microwave irradiation method. The Pd(II)/GO was made by impregnation methods of palladium precursors in solution phase and was subsequently reduced to Pd/G by microwave irradiation. The morphological and chemical structure of the Pd/G was characterized by XRD, SEM, ICP-MS, EDS, and TEM. It was found that the graphene-based Pd catalyst showed the highest catalytic performance among Pd/Y, Pd/MCM-41, and Pd/G catalysts. This is attributed to the smaller particle size and higher dispersions of Pd nanoparticles on the graphene surface. The catalytic HDC of chlorophenols was investigated. For HDC reaction, 100 ppm solution of chlorophenols such as 4-chlorophenol, six isomers of dichlorophenol, and 2,3,5-trichlorophenol in isopropanol was treated with catalyst and base, such as Na₂CO₃ and K₂CO₃, under a hydrogen gas at ambient pressure. The progress of the chlorophenol decomposition was analyzed with GC. All chlorophenols were completely decomposed within 2 h in the 3 % Pd/G catalyst. The reaction pathway of chlorophenols was elucidated from the conversion of chlorophenols and selectivities of products. The reuse of the catalyst was also studied. The performance of the recycled catalyst in HDC reaction up to six successive runs was observed.     

Determination of Formaldehyde with a Platinum–Palladium–Graphene Nanocomposite Glassy Carbon Electrode

The oxidation of formaldehyde on a platinum (Pt)–palladium (Pd)–graphene nanocomposite glassy carbon electrode prepared by chemical reduction was characterized in 0.5?M sulfuric acid. The surface and morphology of the catalyst were characterized by transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. Bimetallic Pt–Pd nanoparticles were uniformly dispersed on the graphene sheets. Energy-dispersed X-ray spectroscopy was used to characterize the metal composition of the nanocomposite. The electrocatalytical characteristics of the modified electrode were investigated by cyclic voltammetry. The results show that the electrode displayed high activity for the oxidation of formaldehyde in sulfuric acid with a linear relationship from 4.50?µM to 0.180?mM and a detection limit of 2.85?µM. The low detection limit, wide linear dynamic range, and high sensitivity of the modified electrode suggests further applications.     

Well-dispersed high-loading pt nanoparticles supported by shell-core nanostructured carbon for methanol electrooxidation

Shell-core nanostructured carbon materials with a nitrogen-doped graphitic layer as a shell and pristine carbon black particle as a core were synthesized by carbonizing the hybrid materials containing in situ polymerized aniline onto carbon black. In an N-doped carbon layer, the nitrogen atoms substitute carbon atoms at the edge and interior of the graphene structure to form pyridinic N and quaternary N structures, respectively. As a result, the carbon structure becomes more compact, showing curvatures and disorder in the graphene stacking. In comparison with nondoped carbon, the N-doped one was proved to be a suitable supporting material to synthesize high-loading Pt catalysts (up to 60 wt %) with a more uniform size distribution and stronger metal-support interactions due to its high electrochemically accessible surface area, richness of disorder and defects, and high electron density. Moreover, the more rapid charge-transfer rates over the N-doped carbon material are evidenced by the high crystallinity of the graphitic shell layer with nitrogen doping as well as the low charge-transfer resistance at the electrolyte/electrode interface. Beneficial roles of nitrogen doping can be found to enhance the CO tolerance of Pt catalysts. Accordingly, an improved performance in methanol oxidation was achieved on a high-loading Pt catalyst supported by N-doped carbon. The enhanced catalytic properties were extensively discussed based on mass activity (Pt utilization) and intrinsic activity (charge-transfer rate). Therefore, N-doped carbon layers present many advantages over nondoped ones and would emerge as an interesting supporting carbon material for fuel cell electrocatalysts.     

氢在活性炭、石墨烯和金属有机骨架上的吸附平衡

为比较不同物理吸附材料的结构参数对其储氢性能的影响,制备和选取了具有超高比表面积的活性炭、石墨烯以及金属有机骨架（MOFs）作为低温吸附储氢的典型材料。首先,利用77 K下氮气在材料上的吸附数据确定了其BET比表面积以及孔径分布的主要结构参数。其次,利用3Flex全自动微孔吸附仪在77-87 K测试了0-0.1 MPa低压下氢在各材料上的吸附量,而后在0.1-8 MPa高压条件下利用PCTPro测试了氢在各材料上的过剩吸附量。最后,分析了各材料的储氢量与其结构参数间的关系。结果表明,在低压下,影响物理吸附材料储氢量的主要因素为孔径分布小于1 nm的微孔;而高压下,氢在多孔材料上的最大过剩吸附量与材料的BET比表面积呈正相关关系,斜率为0.0059 mmol/m²。     

Boron‐Double‐Ring Sheet,Fullerene, and Nanotubes: Potential Hydrogen Storage Materials

Similar to carbon‐based graphene, fullerenes and carbon nanotubes, boron atoms can form sheets, fullerenes, and nanotubes. Here we investigate several of these novel boron structures all based on the boron double ring within the framework of density functional theory. The boron sheet is found to be metallic and flat in its ground state. The spherical boron cage containing 180 atoms is also stable and has I symmetry. Stable nanotubes are obtained by rolling up the boron sheet, and all are metallic. The hydrogen storage capacity of boron nanostructures is also explored, and it is found that Li‐decorated boron sheets and nanotubes are potential candidates for hydrogen storage. For Li‐decorated boron sheets, each Li atom can adsorb a maximum of 4 H₂ molecules with g_d=7.892 wt %. The hydrogen gravimetric density increases to g_d=12.309 wt % for the Li‐decorated (0,6) boron nanotube.     

Reversible chemical switches of functionalized nitrogen-doped graphene field-effect transistors

Nitrogen doping is a promising way to modulate the electrical properties of graphene to realize graphene-based electronics and promise fascinating properties and applications.Herein,we report a method to noncovalently assembly titanium(Ⅳ) bis(ammoniumlactato) dihydroxide(Ti complex) on nitrogen-doped graphene to create a reliable hybrids which can be used as a reversible chemical induced switching.As the adsorption and desorption of Ti complex in sequential treatments,the conductance of the nitrogen-doped graphene transistors was finely modulated.Control experiments with pristine graphene clearly demonstrated the important effort of the nitrogen in this chemical sensor.Under optimized conditions,nitrogen-doped graphene transistors open up new ways to develop multifunctional devices with high sensitivity.     

Facile approach to the electrochemical synthesis of palladium-reduced graphene oxide and its application for Suzuki coupling reaction

Electrochemically codeposited palladium nanoparticles (Pd NPs) and reduced graphene oxide (ERGO-Pd) were used as catalyst for Suzuki cross coupling reactions. The catalyst was characterized by various analytical techniques. The mean particle size of Pd was found to be 5.7 ± 1.8 nm. The ERGO-Pd catalyst demonstrated excellent catalytic activity and recyclability for Suzuki cross coupling reactions. The remarkable reactivity of the ERGO-Pd catalyst toward cross-coupling reactions is attributed to the high degree of the dispersion of Pd NPs on reduced graphene oxide with narrow size distribution from 3 to 9 nm.     

Stabilization of Palladium Atoms in Nitrogen-Doped Porphyrin-Like Fragments of Carbon Nanofibers

The paper considers the system of nitrogen-doped carbon nanofibers (N-CNFs) with palladium atoms deposited on their surfaces. The concentration of deposited palladium varied in the interval of 0.05-0.6 wt.%. The state of palladium was studied with the methods of quantum chemistry, electron microscopy, CO adsorption, and EXAFS. Carbon structures that contain porphyrin-like defects with four nitrogen atoms in the graphene layer interact strongly with palladium atoms and therefore can be stabilization centers of atomic palladium.